1. Field of the Invention
The present invention relates to a head clamping apparatus for a magnetic disk tester that tests the electromagnetic transducing characteristics of a magnetic disk and magnetic head that are essential parts of a hard disk drive. In particular, the present invention relates to a head clamping apparatus for positioning a magnetic head onto a target track on a magnetic disk and measuring the write/read characteristics of the magnetic head, and to a magnetic disk tester provided with a head clamping function.
2. Description of the Related Art
The performance of hard disk drives is improving, and to cope with it, the performance of testers for testing the electromagnetic transducing characteristics of magnetic disks and magnetic heads used for the hard disk drives must be improved.
To deal with increasing track densities in the hard disk drives, magnetic heads must have narrow cores. To correctly measure the characteristics of the magnetic heads with narrow cores, a tester capable of accurately positioning a magnetic head onto a target track on a magnetic disk is needed. Improving the positioning accuracy of a magnetic head is usually achieved by combining a coarse stage driven by a pulse motor or an ultrasonic motor with a micromotion stage driven by a piezo-element.
FIGS. 1 to 3 show a magnetic disk tester 101 according to a related art. The tester 101 has a drive controller (not shown) and a flat base 103. On the base 103, a spindle motor housing 107 incorporates a spindle motor 105. The spindle motor 105 drives a disk clamp 109 arranged on the housing 107. A top end of the disk clamp 109 clamps and unclamps a magnetic disk 111.
On the base 103, a coarse stage (X-stage) 117 is arranged adjacent to the disk clamp 109, to move magnetic heads 113 and 115 along an X-axis that is horizontal in FIG. 1. The coarse stage 117 is driven by an ultrasonic motor 119 along a ball screw (not shown) that extends along the X-axis.
On the coarse stage 117, a segment gear 121 is flatly fixed in parallel with the magnetic disk 111. The segment gear 121 has a semicircular periphery where a rack 123 is formed. A head loader 127 has a pinion (not shown) that meshes with the rack 123 and is driven by a motor (not shown).
The down-face and up-face magnetic heads 113 and 115 are attached to a head clamp 125 installed on the head loader 127. The head loader 127 is movable along a semiarc path on the segment gear 121. In FIG. 1, the magnetic heads 113 and 115 and the rotation center of the magnetic disk 111 are on the same line extending along the X-axis.
Referring to FIGS. 2 and 3, the head loader 127 has a base where a piezo-actuator 129 is arranged to minutely move the head loader 127 along the X-axis. The head clamp 125 has an upper clamp 131 and a lower clamp 133. The upper clamp 131 is removably attached to an upper fitting base 135 that is vertically movable. The lower clamp 133 is removably attached to a lower fitting base 137 that is vertically movable. A front end of the upper clamp 131 has a clamping part 139 to clamp a suspension 141. A front end of the suspension 141 holds the magnetic head 113. A front end of the lower clamp 133 has a clamping part 143 to clamp a suspension 145. A front end of the suspension 145 holds the magnetic head 115. The suspensions 141 and 145 are connected to leads 147, respectively.
The head loader 127 incorporates a driver to separately move the upper and lower clamps 131 and 133 in vertical directions. Namely, the magnetic heads 113 and 115 are moved toward and away from the magnetic disk 111 from above and below the magnetic disk 111.
To test the characteristics of the magnetic heads 113 and 115 with the tester 101, the magnetic disk 111 is rotated by the spindle motor 105 to a predetermined speed. The coarse stage 117 is moved along the X-axis across the tracks of the magnetic disk 111, to position the magnetic heads 113 and 115 onto a target location.
Referring to FIG. 4, an axis of the suspension 141 (145) passing through the magnetic head 113 (115) is provided with a skew (offset) angle with respect to a tangent of a track of the magnetic disk 111. The magnetic heads 113 and 115 each arranged at a front end of an HGA (head gimbal assembly) are vertically adjusted by the upper and lower clamps 131 and 133 of the head loader 127, so that the magnetic heads 113 and 115 may each be separated from the magnetic disk 111 by a predetermined flying height.
The magnetic heads 113 and 115 are minutely moved in a radius direction of the magnetic disk 111 crossing a track, to carry out a track profile test or an error rate test (bathtub characteristic test). During the test, the piezo-actuator 129 is activated to minutely shift the magnetic heads 113 and 115, to improve the positioning resolution of the magnetic heads 113 and 115.
A thermal drift causes an off-track error in the positions of the magnetic heads 113 and 115, and therefore, must be corrected. To achieve this, there is a tester provided with a closed-loop feedback system employing a servo burst signal. Such a feedback system is well-known in hard disk drive technology.
FIG. 5 shows a magnetic head/disk tester disclosed in Japanese Patent Laid Open Publication No. 2000-322850. This tester has a base 243 supporting a carriage (coarse stage) 230. The carriage 230 is guided on horizontal rails 236 and 238 in an X-axis direction as indicated with an arrow mark A.
The carriage 230 supports an outer ring 235 whose center is around an intersection of the X- and Y-axes of a horizontal coordinate system defined on the carriage 230. The outer ring 235 supports an inner ring 233. The inner ring 233 supports and moves a magnetic head support 232 that holds a magnetic head 234 to be tested. The carriage 230 is linearly driven by a step motor 239 along a guide screw 241 that extends along the X-axis. The guide screw 241 engages with an intermediate block 241A that is slidable on horizontal rails 241B and 241C extending along the X-axis. The carriage 230 is also driven by a piezo-actuator 237 along the X-axis with respect to the block 241A. Another step motor (not shown) is used to turn the inner ring 233, magnetic head support 232, and magnetic head 234 around an axis perpendicular to the surface of FIG. 5 relative to the outer ring 235 and carriage 230.
Linear encoders 240 and 242 are arranged on each side of the carriage 230. Each of the encoders 240 and 242 consists of a fixed part 240a (242a) attached to the base 243 and a movable part 240b (242b) attached to the outer ring 235. A present position of the magnetic head 234 is acquired from an arithmetic average of values read from the encoders 240 and 242.
The base 243 has a spindle 244 for rotating a magnetic disk 231 around a vertical axis. The spindle 244 has an optical encoder (not shown) to generate a series of sector pulses in response to angular positions of the magnetic disk 231.
FIG. 6 shows the details of a position controller 249 of the tester of FIG. 5. The operation of the position controller 249 will briefly be explained. To correct a thermal drift, servo burst patterns are written in a magnetic disk beforehand. A servo analyzer 245 detects the servo burst patterns and provides a corresponding signal. The linear encoders 240 and 242 provide signals indicating the position of the carriage 230. The signals from the servo analyzer 245 and linear encoders 240 and 242 are processed, and a result is sent to the piezo-actuator 237 to drive the carriage 230.
Namely, the related art employs the linear encoders 240 and 242 as a first information source and the servo burst patterns as a second information source uses them for a feedback loop.
Signals from the first information source, i.e., the linear encoders 240 and 242 indicate the position of the magnetic head 234 on the magnetic disk 231 and do not include a thermal drift. The moving range of the first information source is relatively wide to cover the whole area of the magnetic disk 231, and therefore, data from the first information source is used to move the magnetic head 234 from one position to another.
Signals from the second information source, i.e., the servo burst patterns recorded on the magnetic disk 231 indicate the position of the magnetic head 234 on the magnetic disk 231 and involve temperature conditions. The second information source covers a narrow area around a track on the magnetic disk 231, and therefore, data from the second information source is used to keep the magnetic head 234 at an instructed position.